Based on previous family studies, an autosomal recessive disease with alleles A and a is suspected to be linked to an RFLP marker. The RFLP marker has four alleles, R₁, R₂, R₃, and R₄. The accompanying pedigree shows a three-generation family in which the disease is present. The gel shows the RFLP alleles for each family member directly below the pedigree symbol for that person. After determining the genotypes for the RFLP and disease gene for each family member, answer the following questions.
What is the most likely arrangement of syntenic alleles for the RFLP and the disease gene in I-1 and I-2?

Question

Based on previous family studies, an autosomal recessive disease with alleles A and a is suspected to be linked to an RFLP marker. The RFLP marker has four alleles, R₁, R₂, R₃, and R₄. The accompanying pedigree shows a three-generation family in which the disease is present. The gel shows the RFLP alleles for each family member directly below the pedigree symbol for that person. After determining the genotypes for the RFLP and disease gene for each family member, answer the following questions.

What is the most likely arrangement of syntenic alleles for the RFLP and the disease gene in I-1 and I-2?

Pedigree chart of a three-generation family with RFLP gel results showing alleles R₁ to R₄ for each member.

What is the most likely arrangement of syntenic alleles for the RFLP and the disease gene in I-1 and I-2?

Accepted Answer

Hi, everybody. Welcome back. Let's look at our next problem in a study of pea plants. An R F LP marker was identified and found to be linked to the gene for purple flowers which is dominant over the gene for white flowers. The RFLP marker has two alleys A and B A genetic cross between two heterozygous purple flowered plants produce the following offspring and we have a table with the genotype and the number of offspring. So genotype A A 23 A B 46 B B 23 then total offspring 92 assuming the recombination frequency between the R F LP marker and the purple flower gene is 15% which of the following shows the correct gene map. And we have four different answer choices with different distances marked between the R F LP marker and the purple flower gene along with distances on the outside of them. Well, sometimes in multiple choice questions or just questions in general, we're given more information than we actually need. And part of solving the problem is figuring out what information is necessary to solve the problem and what information is extraneous. And this is a good example here, if we focus in on the question, we're being asked, we're looking for the correct gene map. So we'd say what is the distance between the genes and what order are they in? Now, in this case, we only have two genes. So order doesn't really matter because all you have is information is the distance between them. If you had three genes or more, then part of your problem would also be putting them in the order they occur. When we're looking at distance between genes, we know that distance is proportional to recombination frequency. And in this case, we are given the recombination frequency between the two genes. The one being the R F LP marker and the other, the gene for flower color and that recombination frequency is 15%. So we have all the information we need to talk about these two genes and the distance between them. We don't need that entire table. We don't need to know what the genotypes are a number of offspring because the that information isn't necessary. All we need is that recombination frequency. So since our recombination frequency is 15% we know that the distance between the genes is 15 centam organs. So that's just really straightforward. And when we look at our answer choices, we see that only one of them has a distance of 15 cent of organs between the two genes. And that would be choice C which says purple flower gene 15 centam organs, R F LP marker and then 85 centam organs. When we look at our other answer, choices, choice A has a distance of 85 cent organs between the two genes. That would be 85% is the percent of offspring that would have parental genotypes. 15 centam organs is the re percent of offspring with recombinant genotypes and therefore reflects the distance between them. So that's why choice A is not correct. Choice B which says 75 centam organs, R F LP marker purple flower gene does not show that distance between them that we know from our problem. So choice B isn't correct. And choice D shows a distance between the two genes of 37 centam organs. So that's not correct either. So again, the distance the between the two genes which we know from our problem leads us to the correct gene map here. Of choice C purple flower gene, 15 centam organs R F LP marker 85 centam organs. See you in the next video.

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Key Concepts

Autosomal Recessive Inheritance

Restriction Fragment Length Polymorphism (RFLP)

Syntenic Alleles